The prior art flat-plate solar energy collectors generally consist of a number of transparent panes and an absorbing surface, the surface in turn is of metal coated with a suitable black absorbing material. A liquid or gas is passed either in front, behind, or around the absorbing surface to extract energy from the absorbing surface. The energy absorbed is then transported by the liquid or gas to the point of application. Suitable insulation is placed behind the collector and along the edges to reduce heat loss. Improvements have been made in the performance of flat-plate collectors by the use of selective black coatings which have a high rate of solar absorption and low infrared emittance. Other improvements include evacuating the gas between the transparent panes and the absorbing surface. In some instances a honeycomb structure is utilized to reduce conduction losses.
Other prior art solar energy absorption systems utilize tubing -- but the tubing is either metal or of clear plastic coated with a black absorbing material. In operation these collectors have a nearly uniform temperature over the entire surface; accordingly, being susceptible to radiant heat losses.